As far as applicants know, the reaction on which the process of the present invention is based has never been described or suggested by the prior art.
According to the art--however through reactions not related to the one of this invention--3,5-dienoic acids and substituted derivatives thereof can be prepared by means of alternative processes based on the Witting synthesis starting from aldehydes and organic phosphorous compounds in stoichiometric amounts.
Nevertheless, techniques of such type require a preliminary preparation of suitable aldehydes, which are sometimes difficult to prepare or retrieve and the stoichiometric use of phosphorated intermediates, which are objectionable from the viewpoint of the compatibility of the effluents with the present environmental protection requirements and with the financial burden connected thereto, which render such techniques substantially non-applicable on an industrial scale.
Finally, catalytic processes are known, which are useful to prepare 3,5-dienoic acids, optionally aryl-substituted, by reaction of substituted allyl halides with acetylene and carbon monoxide in hydroxylated solvents in the presence of nickel carbonyl or precursors thereof, followed by isomerization.
Said methods are of minor industrial importance due to the use of nickel carbonyl derivatives and of carbon monoxide. Furthermore, they are not suitable for industrial applications owing to the high toxicity of the described conditions.